Add --unreferenced-only flag to acr purge

[escherstair]

I can use acr purge to delete some manifests.
I can add either --untagged or --untagged-only flag to limit the delete to manifests which don't have any tag.
Thsi si ok.

But sometimes I have manifests that have no tags, but they have a referrer artifact (in a OCI artifact graph).
And I would like avoiding to delete this manifests.

This is the reason why I ask for a --unreferenced-only flag (to be used alone or together with --untagged or --untagged-only) to delete only manifests which don't have any referrer artifacts.

[estebanreyl]

I see. I am not sure this is the way I would go about it but I do think we need to introduce some way to manage and purge images dependent on their referrer situation or even introduce a way to cleanup their referrers. Can you elaborate a bit on why you want to avoid deleting any image with referrers attached? This might help us better define such a scenario.

[escherstair]

Hi @estebanreyl thanks.
I try to describe what is my scenario:

• in ACR I have some repos that contain container images
• in ACR I have other repos that contain docker-compose.yml published as an application (every docker-compose.yml contain specific tags of container images)
• to simplify handling the several artifact in ACR I use ORAS so that I attach referrers:
  • every time I publish a docker-compose.yml, I attach a new referrer to every container images it uses
  • in this way I can easily use ORAS to generate a usage graph
• when an application is no more needed (it's only for testing, or whatever reason) I do the following:
  • I delete the docker-compose.yml application
  • I remove the corresponding referrers from all the referred container images

In this way, a docker image without any referrer means that no application uses it anymore.
And so I can delete it safely (saving space on ACR).